Ionizing Radiation Effect on Structure and Long-term Adhesion in Enamel-dentin

Objectives: Radiotherapy is widely used treatment for head/neck cancer. Radiation damage on the composition and mechanical properties of dental hard tissues and further impact on dental restorations is still unclear. Thus, this study assessed the effects of ionizing radiation doses on the mineral/organic structures, microhardness (VHN) of enamel and dentin, and long-term bond strength stability of etch-and-rinse(ER) and self-etch(SE) adhesive strategies.
Methods: Freshly extracted human-third-molars were exposed to 0, 20, 40, and 70 Gy radiation doses, sectioned and prepared for knop hardness (VHN) and chemical composition using ATR-FTIR spectroscopy. Dentin and enamel were prepared for resin adhesion protocol and evaluation using microtensile bond-strength test (uTBS) test (immediate time[IM] and 12-month[12M] period) for dentin; and microshear bond-strength(uSBS) test for enamel [IM]. Mann–Whitney U tests, three- and two-way analyses of variance (Tukey post-hoc test, a=0.05) were used.
Results: There was a significant decrease (p<0.05) in the amide III/phosphate ratio of enamel and dentin, after 20 and 40 Gy doses, respectively. The crystallinity index was significantly reduced for both tissues with 70 Gy (p<0.05). Microhardness of dentin and enamel decreased significantly at all radiation doses (p<0.05). In dentin, the uTBS of ER and SE was not affected with exposure until 40 Gy; however, the effect of all does was noted after 12M. The ER strategy is greater and more stable than SE with doses up to 40 Gy. The TBS of ER decreased 27% after 12M, with a similar performance of SE at the same doses. In enamel, the ER achieved the highest uSBS and high enamel cohesive fractures (40.5 to 52.6%).
Conclusions: All radiation doses induced structural and composition changes to enamel and dentin, decreased the microhardness. Doses of 40Gy or above impaired bond strength over time. The ER strategy has better adhesive performance.